The invention relates to a charge sensor, more particuarly for a charge transfer device, which includes two cross-coupled MOS transistors T.sub.1 and T.sub.2 each having a source, a drain and a gate, the gate of T.sub.2, and the drain of T.sub.1 being connected to a first junction A.sub.1 and the gate of T.sub.1 and the drain of T.sub.2 being connected to a second junction A.sub.2, while the sources of T.sub.1 and T.sub.2 are connected to a third junction A.sub.3. The charge sensor also includes two load MOS transistors T.sub.3 and T.sub.4, each having a source, a drain and a gate, the sources of T.sub.3 and T.sub.4 being connected to A.sub.1 and A.sub.2, respectively, aand the drains of T.sub.3 and T.sub.4 being connected to a fourth junction A.sub.4, while the gates of T.sub.3 and T.sub.4 are coupled to signal supply means.
A positive and a negative current supply lead are provided for passing a current between the junction A.sub.3 and A.sub.4, and a fifth MOS transistor T.sub.5 is provided which acts as a switch and has a gate which is connected to a clock voltage source for applying the clock voltage for the intermittent energization of the sensor.
A sixth and a seventh MOS transistor each having a source, a drain and a gate are also provided, the drain of T.sub.6 being connected to A.sub.1 and the drain of T.sub.7 being connected to A.sub.2, while the sources are connected to the current supply lead associated with A.sub.3 and the gates are connected to a clock voltage source for intermittently opening and closing the transistors T.sub.6 and T.sub.7.
The invention further relates to a charge transfer device which is provided with such a charge sensor.
It should be noted that in the following description a transistor is considered to be closed when it is in a conductive state and is considered to be opened when it is in a non-conductive state. The transistors T.sub.1 -T.sub.4 constitute a flipflop circuit with the transistors T.sub.1 and T.sub.2 as driver trabsistors and the transistors T.sub.3 and T.sub.4 as loads. The transistor T.sub.5 serves to energize the flipflop when new signal charges to be read are supplied. The transistors T.sub.6 and T.sub.7 serve to reset the junctions A.sub.1 and A.sub.2 after reading. The output signals can be derived at the junctions A.sub.1 and A.sub.2.
A circuit arrangement of the kind mentioned above is particularly suitable for reading information in a CCD storage, in which the digital information stored in the storage can be applied to one input gate and a reference level halfway between the "0" level and the "1" level can be applied to the other input gate. Such a charge sensor is described inter alia in U.S. Pat. No. 3,983,413 of Gunsager et al. In this known circuit arrangement, the junction A.sub.3, i.e. the sources of the driver transistors, is applied to a fixed potential, i.e. the earth, while the junction A.sub.4, i.e. the drains of the load transitors, is connected to the positive supply through the aforementioned switching transistor T.sub.5. Another prior art circuit is shown in IEEE JSSC, Vol. SC-12, No. 4, August 1977, pp. 335-343.
In a known circuit arrangement having a configuration as shown in Gunsager, during operation a number of problems may arise, which adversely affect the reliability of the sensor. Due to the fact that the switching transistors T.sub.5 is connected to the load transistors T.sub.3 and T.sub.4, the transistors T.sub.3 and T.sub.4 each time have to be raised from 0 V to the high supply voltage (for example 5 V). Due to capacitive couplings, the gates of T.sub.3 and T.sub.4 and hence also the output zones of CCD channels connected to these gates, will perform a corresponding voltage jump. A second problem resides in the control of the load transistors T.sub.3 and T.sub.4. The voltage by which their conduction is determined at the instant of activation depends inter alia upon the supply voltage, the transistor threshold voltage, the signal charge and cross-talk voltages. Due to the fact that in general the conduction in these transistors is high, the conduction difference is comparatively small, as a result of which the aforementioned varying conditions can seriously and adversely affect the reliability of the circuit arrangement.